This invention pertains generally to the art of apparatus and methods for applying cords to a rotating structure, and more specifically to apparatus and method for producing elastomeric belts with precise cord length and cord tension.
Traditional methods of applying cords to a rotating mandrel involved a cylindrical mandrel of minimal compliance, meaning the dimensions of the mandrel, especially the diameter and circumference, are essentially constant. The mandrel may be a rigid cylinder, in which case the cord length is controlled by selecting a cylindrical mandrel with the correct circumference. Other mandrels are not cylinders, and the invention disclosed herein applies to such mandrels as well.
In some prior art mandrels, the mandrel circumference is adjusted by applying or removing layers of material from its surface. Other mandrels have radially telescoping elements which form a series of arcs approximating a circle. In all of these, the cord is applied using a guide wheel which controls the cord tension as accurately as practical in a demand feed mode. The length of cord per revolution of the mandrel is dependent on the cylinder circumference and, therefore, on the manufacturing tolerances of the cylinder.
Mandrels are often used in the construction of elastomeric belt products, such as timing or drive belts for automotive applications. Most belt designs also require layers of other belt materials be wound onto the cylinder before the cord. The thickness, hardness, and temperature tolerances of these materials may also affect cord length.
The present invention controls cord length independently of the tolerances of the cylinder or the underlying layers. Furthermore, the present invention is capable of controlling cord length in a highly accurate manner, with accuracies to 30 parts per million possible. This is of particular importance in making toothed timing belts where a cord length error will result in improper meshing of teeth and premature tooth or belt failure.
Another advantage of the present invention is that the helical cord structure made by the present invention can be removed easily from the cylinder without loss of length accuracy or distortion of the helix dimensions. This allows the belt containing the cord to be formed by internal pressure in an external mold like a tire mold, or in a press, rotocure, or sectional cure device. The belt is easily removable due to the collapsibility of the mandrel. Allowing the mandrel to collapse releases tension in the cord and provides enough clearance for easy removal of the belt from the mandrel.
Timing belts are traditionally made on cylindrical molds having tooth forms on the outer surface which are parallel to the cylinder axis. A layer of fabric, rubber, plastic, or other flexible material is placed over the cylinder. The cord is wound over the outside of the assembly. Additional materials may be placed over the cord. The belt is formed by applying inwardly radial pressure from a diaphragm during the curing process. The finished product is removed by sliding it axially to disengage the mold teeth from the belt teeth. This process can work for belts with axial teeth or belts with a single set of helical teeth, but it cannot work for an interrupted tooth such as a herringbone, dual helical, or zigzag tooth because belts with these forms of teeth cannot slide axially off the mandrel.
The present invention allows these products to be made with an external rather than an internal mold, while still retaining cord length accuracy. It also allows these products to be made with flat sectional molds while retaining cord length accuracy. Both of these methods allow the belt teeth to be disengaged from the mold by motion approximately perpendicular to the mold surface. This allows the interrupted tooth forms to be removed from the mold.
The present invention contemplates a new and improved method of producing belts with precise cord length and tension which is simple in design, effective in use, and overcomes the foregoing difficulties and others while providing better and more advantageous overall results.
In accordance with the present invention, a new and improved method of producing belts with precise cord length and tension is provided.
The invention is a method and apparatus for applying accurate lengths of cord to a rotating mandrel by using a geared feed capstan. The geared feed capstan measures and meters out a selected length of cord for each revolution of the mandrel. All real materials suitable for winding, including cords or wires, are elastic or stretchable, so that an accurate description of the length of the cord to be applied must also specify the tension in the cord when its length is measured. The feed capstan measurement and metering accuracy is affected by the tension of the cord entering and exiting the feed capstan. This necessitates measuring and controlling the cord tension. The exiting tension is controlled by the expansion of the mandrel. The entering tension is held constant by a tension control capstan, but any other means that maintains accurate entering tension is also suitable. In the disclosure, the exiting cord tension control is achieved by the expanding mandrel and the tension sensing load cells which in part control the expansion. The concept of primarily controlling cord length and secondarily controlling cord tension is a key element of the invention.
For example, other cord winding machines use cord tension as the control parameter. As the mandrel rotates, the length of cord is determined by the mandrel circumference, a procedure called xe2x80x9cdemand feedxe2x80x9d for the purposes of this disclosure. The length of the cord is dependent on the mandrel circumference and the tolerances of that circumference. There is no means of accurately determining the length of cord so applied.
The function of the apparatus disclosed herein may be inverted (so that the cord length is secondarily controlled and cord tension is primarily controlled) and the apparatus will still provide improvements and benefits over the prior art. The load cells which control the expansion of the flexible diaphragm can instead be used to control cord tension directly, and the feed capstan can be used as an accurate length measuring device rather than as a measuring and metering device. The length measured at the feed capstan can then be used to control the mandrel inflation to obtain the desired metered length of cord.
In accordance with the present invention, there is disclosed an apparatus for applying a cord to a rotating structure, the apparatus including a capstan for regulating the length of the cord; supplying means for supplying the cord to the capstan; holding means for holding and rotating the rotating structure; and applying means for applying the cord from the capstan to the rotating structure on the holding means.
According to another aspect of the present invention, the apparatus for applying a cord to a rotating structure further includes a first capstan between the supplying means and the applying means; and, a second capstan between the first capstan and the applying means.
According to another aspect of the present invention, the applying means includes a laying wheel and, a second tension sensor, the second tension sensor being located between the laying wheel and the second capstan.
According to another aspect of the present invention, a method for applying a cord to a rotating structure is provided. The method includes the steps of supplying the cord to a capstan via supplying means; positioning the cord around the capstan, thereby applying tension to the cord; feeding the cord to an applying means; and, applying the cord around the rotating structure, the rotating structure being connected to a mandrel means. The rotating structure is expandable.
According to another aspect of the invention, the method further includes the cord being positively fed to the mandrel according to a defined algorithm where said algorithm is based on a shape, circumference and rotational speed of said mandrel.
According to one aspect of the invention, an apparatus for accurately applying a cord to a rotatable mandrel includes means for dynamically adjusting the circumference of the mandrel in response to a control input. The means for adjusting is an inflatable diaphragm mounted on an outer surface of the mandrel.
According to another aspect of the invention, the apparatus further includes control means which includes a control valve capable of dynamically adjusting the mandrel circumference by selectively inflating or deflating the diaphragm in response to feedback control input of a measured cord tension.
According to another aspect of the invention, the apparatus includes control means which includes a control valve and tension control means wherein the tension control means is an electronically geared tension control capstan.
According to another aspect of the invention a cord-laying means for laying the cord on said mandrel includes a cord-laying wheel which isolates radially directed forces from said mandrel.
According to another aspect of the invention the belt can be corded on first and second pulleys. The first and second pulleys being spaced a center distance apart, and the center distance being selectively adjustable to control cord tension in the cord. The center distance between the first and second pulleys is dynamically adjustable to control cord tension in the cord during said positive-feeding of the cord onto the mandrel.
According to another aspect of the invention a position-determining means, namely an encoder, is operatively associated with the motor and shaft which rotates the mandrel.
According to another aspect of the invention, a method of accurately applying a cord to a rotatable mandrel is provided. The comprising the steps of rotating a mandrel, the mandrel having means for dynamically adjusting a circumference of the mandrel in response to a control input, the means being an inflatable diaphragm mounted on an outer surface of said mandrel, and sending the control input to the means to adjust the circumference of said mandrel in order to maintain a desired cord tension.
According to another aspect of the invention, a method of accurately applying a cord to a rotatable mandrel is provided. The comprising the steps of rotating a mandrel, feeding cord to said mandrel, laying the cord on said mandrel, and, isolating radially directed forces from circumferentially-directed forces.
One advantage of the present invention is its ability to apply a cord at a known length and tension to a rotating structure according to a defined algorithm, such application being made independently of the shape, size, and speed of the rotating structure.
Another advantage of the present invention is its use of an accurate feed capstan in conjunction with a means of accurately controlling tension into and out of the capstan.
Another advantage of the present invention is the use of a tension capstan to control the tension of a cord into the feed capstan.
Another advantage of the present invention is its control of the tension from the feed capstan to the rotating structure by making the rotating structure radially compliant to the cord being wound.
Another advantage of the present invention is its ability to dynamically adjust the radius of the mandrel as it rotates using measured tension feedback to adjust the radius to achieve desired cord tension.
Another advantage of the present invention is the use of a rigid cord laying wheel to accurately control the cord position on the mandrel and to separate the radial forces that arise from laying the cord from the desired forces which result from the tension in the cord.
Another advantage of the present invention is the use of timing belt or chains to positively feed a cord onto a belt slab which is rotating on two or more pulleys.
Another advantage of the present invention is its ability to adjust the center-to-center distance between pulleys to control cord tension during positive feeding of the cord.
Still other benefits and advantages of the invention will become apparent to those skilled in the art upon a reading and understanding of the following detailed specification.